In control of power equipments, production equipments in factories, and robots, a number of processes are calculated under real-time restrictions that the processes should be finished in a prescribed period. Among these calculations, a relative complex calculation such as device state estimation or disorder clustering includes iterative calculations and has characteristics that the processing time changes greatly according to the amount of data used and the property thereof.
In particular, a mission critical system like a social infrastructure that operates for a long period without stopping has to complete calculations while satisfying the real-time restrictions in order to guarantee safety even when the number of processes increases in the event of calamity or when a system expansion which was not planned in the original design and development stages occurs.
Patent Literature 1 discloses a technique of changing the level of processes by taking a change in processing time into consideration. This literature discloses a technique of enabling a plurality of stages of calculations to be executed smoothly by switching to approximations based on a congestion state of a queue that stores the calculation results of previous stages and the rate of occurrence of an event that it was not possible to perform a calculation of a subsequent stage in a state where a calculation of the previous stage has not been finished.